1. Technical Field
The present invention is directed to a wireless communication field, and more specifically to a local wireless communication system and method employing frequency-variable signal detection, which may secure a communication channel in a given frequency band by using a spectrum-sensing method.
2. Related Art
In recent years, wireless communication systems have been rapidly grown up owing to the commercialization of mobile telecommunication and technological convergence.
Unlike long-haul telecommunication technologies such as satellite or mobile communications, local wireless access technologies, especially RF/Microwave systems, are different from an image of current simple up/down conversion systems and pursue technological innovation mainly employing wideband, low-power consumption, and efficient distribution of frequency resources.
A good example of the wideband technology is UWB (Ultra Wideband) that has been enjoying its fame as one of highly-ranked wireless technologies for the last ten years.
Since a standard frequency band for UWB was assigned by U.S. FCC, the research and development has been focusing on both IEEE 802.15.3a associated with HR (High-Rate) UWB technologies and IEEE 802.15.4a associated with LR (Low-Rate) UWB.
Wide band technologies in the field of RF/Microwave generally have been treated for simple increment of the bandwidth for system applications. Thus, it has been overlooked for technical environments as a key to technological success, which may be achieved only by researching circuit technologies in point of view of systemic considerations.
Representative HR-UWB camps are the MBOA (multiband OFDM Alliance), which increases a signal bandwidth of OFDM (Orthogonal Frequency Division Multiplexing) as much as necessary for high-rate communications, and DS-CDMA that spreads and uses the entirety of 2 GHz frequency band. In particular, IEEE 802.15.4a standard for LR_UWB is now excluded from next generation USN (Ubiquitous Sensor Network) terminal candidate in a standard competition, because it was shifted to a high-capability, high-cost standard based on IR (Impulse Radio) by high-accuracy additional functions.
Second, RF/Analog circuit-related technologies have been rapidly developed for the last twenty years by overcoming problems with current wireless terminals, such as bulky size and large power consumption thanks to the integration technologies.
At the same time, circuit and system design technologies for low-power applications are required for BioRF, RF Sensor Node, and so on from the demand of recent diversified system environments and circuit technologies.
Pico (10−12) watt RF transceiver and network technologies have been co-researched for sensor nodes in BWRC(Berkeley Wireless Research Center) of UCB (University of California at Berkeley), a representative of the lower power RF technology research organization.
This project named “PicoRadio” partially enjoyed a success in developing low-power RF devices using MEMS and energy scavenging technology that collects energy from natural sources, however, such a success is still limited in developing a few devices and evaluating the possibility of energy scavenging technology.
Accordingly, a new project called “pJoule” has been launched to continue researching low-power, high-efficient systems.
Third, “cognitive radio (CR)” system technology originating from a point of view of efficient reuse of limited frequency resources, primarily focuses on system hardware in which a terminal determines whether to use a spectrum of a wireless transmitting channel to dynamically allocated a channel.
This technology can save costs as well as effectively operate wireless channels by efficient reuse of a frequency resource that is considered as the only medium in wireless communications.
Further, it has an advantage of the capability of developing a new wireless application using a spectrum sensing technology.
However, most of spectrum sensing technologies, which are core technologies of a CR system and have been suggested and studied in IEEE 802.22 standard, have a procedure of down-converting a signal received by a terminal to a base band to identify whether there is a valid signal on a channel by a digital processor or not.
It has some demerits like long processing time and high energy consumption.
Meanwhile, the GEDC (Georgia Electronic Design Center) of Georgia Tech, USA, which is the only institute with spectrum sensing technology in RF Front-End, suggested a technology of identifying whether a spectrum is used or not at relatively high speed through a dual loop process of “Coarse sensing” and “Fine Sensing”.
In Korea, it has been attempted by ETRI, Samsung Electro-Mechanics together with a professor group of GEDC (J. Lasker et al.) to introduce a dual loop technology to CR systems.
Because of adopting precise and accurate dual evaluation, the spectrum sensing technology of GEDC is appropriate for relatively complicated terminal environment requiring high-cost, high-class services, but not for local low-power small systems such as USNs.